I get the message "please remove "-insecure" from the launch options before attempting to connect to a VAC secured server" every time i try to start a regular multiplayer match, and am unable to play, please help if you can

You're doing it wrong. Do not rightclick on the desktop-icon. Go into Steam->Library where you have all your games listed. Rightclick on Left 4 Dead 2 in the list on the left and the "SET LAUNCH OPTIONS" is right there on the first "General" tab.

did not work, should i just redownload L4D2? would not be a huge problem

listen redownloading won't help the problem and don't go to your desktop icon. Like gozu and cease said go to your games list and go to left 4 dead 2 right click it and go all the way until you see a option called Properties and click it. Once you're on the General tab which is on the first tab like cease, there should be an option called Set Launch Options click it and get rid of the "-insecure" and if you still have no clue then i have nothing to say anymore